Problems tracking links to a page which doesn’t exist

My web stats show that my second most popular page in my site is /blog/index.html but unfortunately this page doesn’t exist so instead takes visitors to my 404 page.

I’ve searched through the entire site looking for links to this mystery url and can’t find anything. I’ve had a look at incoming links and can’t find anything there. Any ideas what might be happening here?

My second problem is how to track which pages lead to the 404 in the first place. On my site I have a custom 404 page with a piece of google analytics code to tell me which page generated the 404. But I can’t do this on the blog because the 404.php page doesn’t have any html body tags to place the code in. how can I track which pages lead to the error using wordpress?